High Resolution Photoelectron Spectroscopy in Hard X-ray
and low hn below 11.7 eV
S.Suga
Graduate School of Engineering Science, Osaka
University,
1-3 Machikaneyama, Toyonaka,
Osaka, Japan
It is nowadays well
known that bulk sensitive photoelectron spectroscopy (PES) is necessary to
probe the bulk electronic structures of solids, which have much different
surface electronic structures. Strongly correlated electron systems are such
examples.
In order to overcome the surface
sensitivity of the conventional PES with the photoelectron kinetic energy EK
in the range of 15-200 eV, soft X-ray PES was
extensively employed for EK in the range of 500-1000 eV, providing the clues to genuine bulk electronic
structures. It is found, however, that the bulk components are still ~50-70% of
the whole spectral weight in the valence band.
Then the necessity of the hard X-ray PES
(HAXPES) in the hn region above 6 keV is
recognized. Although the photon flux are higher in the X-ray than in the soft
X-ray because of the use of the Bragg diffraction crystal monochromators,
the photoionization cross sections are orders of
magnitude smaller in HAXPES, though the bulk spectral weight can be >95%. In
addition, the recoil effects are recognized on photoelectron emission from the electronic
structures derived from light elements in some materials. The usefulness of
HAXPES and the limit by recoil effects are discussed.
In the extremely low energy PES (ELEPES) by
use of Xe, Kr, and Ar
microwave excited electron cyclotron resonance lamp, high total-resolution
(<5meV) is easily achieved. This system is briefly explained and studies of
strongly correlated materials are discussed and the comment is given on the
bulk sensitivity of this technique.
The materials covered in this talk range
from Al, Cu to compounds containing Li, V, O, Si as well as alloys containing Sm, Yb.